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arXiv:2105.06748 · npj Quantum Information

Gigahertz measurement-device-independent quantum key distribution using directly modulated lasers

Robert I. Woodward, Yuen San Lo, Mirko Pittaluga, Mariella Minder, Taofiq K. Paraïso, Marco Lucamarini, Zhiliang L. Yuan, Andrew J. Shields

Published Apr 8, 2021• 88 citations
arXivHTMLPDF

Abstract

Abstract Measurement-device-independent quantum key distribution (MDI-QKD) is a technique for quantum-secured communication that eliminates all detector side-channels, although is currently limited by implementation complexity and low secure key rates. Here, we introduce a simple and compact MDI-QKD system design at gigahertz clock rates with enhanced resilience to laser fluctuations—thus enabling free-running semiconductor laser sources to be employed without spectral or phase feedback. This is achieved using direct laser modulation, carefully exploiting gain-switching and injection-locking laser dynamics to encode phase-modulated time-bin bits. Our design enables secure key rates that improve upon the state of the art by an order of magnitude, up to 8 bps at 54 dB channel loss and 2 kbps in the finite-size regime for 30 dB channel loss. This greatly simplified MDI-QKD system design and proof-of-principle demonstration shows that MDI-QKD is a practical, high-performance solution for future quantum communication networks.

DOI
10.1038/s41534-021-00394-2

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Abstract Measurement-device-independent quantum key distribution (MDI-QKD) is a technique for quantum-secured communication that eliminates all detector side-channels, although is currently limited by implementation complexity and low secure key rates. Here, we introduce a simple and compact MDI-QKD system design at gigahertz clock rates with enhanced resilience to laser fluctuations—thus enabling free-running semiconductor laser sources to be employed without spectral or phase feedback. This is achieved using direct laser modulation, carefully exploiting gain-switching and injection-locking laser dynamics to encode phase-modulated time-bin bits. Our design enables secure key rates that improve upon the state of the art by an order of magnitude, up to 8 bps at 54 dB channel loss and 2 kbps in the finite-size regime for 30 dB channel loss. This greatly simplified MDI-QKD system design and proof-of-principle demonstration shows that MDI-QKD is a practical, high-performance solution for future quantum communication networks.
Measurement-device-independent quantum key distribution (MDI QKD) removes all detector side channels and enables secure QKD with an untrusted relay.It is suitable for building a star-type quantum access network, where the complicated and expensive measurement devices are placed in the central untrusted relay and each user requires only a low-cost transmitter, such as an integrated photonic chip.Here, we experimentally demonstrate a 1.25-GHz silicon photonic chip-based MDI QKD system using polarization encoding.The photonic chip transmitters integrate the necessary encoding components for a standard QKD source.We implement random modulations of polarization states and decoy intensities, and demonstrate a finite-key secret rate of 31 bit=s over 36-dB channel loss (or 180-km standard fiber).This key rate is higher than state-of-the-art MDI QKD experiments.The results show that silicon photonic chipbased MDI QKD, benefiting from miniaturization, low-cost manufacture, and compatibility with CMOS microelectronics, is a promising solution for future quantum secure networks.
Breakthroughs in chip integration technology have accelerated the practical deployment and scalable implementation of quantum key distribution (QKD). On-chip quantum light sources are critical components of fully integrated QKD systems. Measurement-Device-Independent QKD (MDI-QKD) offers significant advantages in network communication by eliminating vulnerabilities to side-channel attacks at the detector side, while relying on high-visibility Hong-Ou-Mandel interference between photons emitted by two independent lasers. Here, we present an innovative design of the silicon-based hybrid integrated self-injection locking (SIL) laser chip that achieves high-frequency-stability operation with the frequency detuning between independent lasers suppressed to within 15 MHz, enabling high-visibility HOM interference in MDI-QKD. Leveraging this design, we experimentally demonstrate a loss-tolerant MDI-QKD system employing the setting-choice-independent correlation security framework explicitly accounting for state-preparation uncertainty. The system achieves a finite-key secret rate of 17 b/s under 34 dB channel loss (or 170-km standard fiber), surpassing previously reported MDI-QKD experiments that incorporated state preparation uncertainty under equivalent transmission loss conditions. Our result makes a promising contribution to practical applications of fully integrated quantum communication networks.
Measurement-device-independent quantum key distribution (MDI-QKD) is a promising path toward practical quantum communication, but current high-performance demonstrations come at prohibitive overhead and isolated environments. Here, we present a high-speed MDI-QKD system operating at an unprecedented repetition frequency of 2.5 GHz and verify its strong noise tolerance by incorporating the advantage distillation method. The secure key is efficiently generated under 425 kHz noise counts, which is 4 orders of magnitude higher than isolated systems. A secure key rate with a kbps level is achieved under 30 dB channel attenuation without bulky, resource-intensive detection devices. Our Letter establishes a complete practical solution for QKD deployment and resolves the persistent difficulty of realizing practical quantum secure networks with advanced security, a high key rate, environmental robustness, and physical compactness.
Quantum key distribution (QKD) can serve large numbers of users with unconditional secure communication, in which measurement-device-independent (MDI) QKD protocol can conveniently enhance realistic security by eliminating all detector side channels. In multi-user scenarios, MDI-QKD networks should meet the requirements of reliability and robustness. Around the issues, we complete a series of work on performance improvement, low-cost deployment, and robust networking. First is to answer how to change the trusted node to the untrusted node with low cost, here we propose and demonstrate an MDIQKD which is compatible with phase encoding BB84 networks, allowing for economical deployment of MDI-QKD networks and reconciliation between high key rate and high realistic security in the same network. Then we make the MDI networks more robust. We design an MDI-QKD networking scheme for multi-user access where more than two users can generate keys synchronously regardless of aligning reference frames and compensating channel disturbance on polarization. Third, we find a general method to distil secure keys from quantum discord, which is different to the previous entanglement-based frameworks of MDI-QKD, allowing imperfect preparation and measurement of quantum states. The series of work can help the practical application of MDI-QKD networks, and promote the development of quantum networks.
Measurement-device-independent quantum key distribution (MDI-QKD), which is immune to all detector side-channel attacks, is the most promising solution to the security issues in practical quantum key distribution systems. Although several experimental demonstrations of MDI-QKD have been reported, they all make one crucial but not yet verified assumption, that is, there are no flaws in state preparation. Such an assumption is unrealistic and security loopholes remain in the source. Here we present a MDI-QKD experiment with the modulation error taken into consideration. By applying the loss-tolerant security proof by Tamaki et al. [Phys. Rev. A 90, 052314 (2014)], we distribute secure keys over fiber links up to 40 km with imperfect sources, which would not have been possible under previous security proofs. By simultaneously closing loopholes at the detectors and a critical loophole---modulation error in the source, our work shows the feasibility of secure QKD with practical imperfect devices.